ATR-20 Instruction Manual
Ameritron Antenna Tuner
2
1.2
Peak Reading SWR/Wattmeter
The ATR-20’s cross-needle meter displays peak or average FORWARD power, peak or average
REFLECTED power, and SWR.
The wattmeter can be used without the tuning network by setting the ANTENNA SELECTOR to any of
three
COAX DIRECT
positions of the antenna selector. The wattmeter is active in all six positions of
the ANTENNA SELECTOR switch.
The ATR-20 must have a power source, or the meter won’t function. Power can be provided by an
external 12 Vdc supply (negative ground only) or an internal 9 Volt “transistor radio” battery. The meter
lamp will not illuminate unless an external supply is used.
Battery life is greatly increased through use of an RF controlled solid state battery switch. After a short
period of inactivity, the battery is electronically disconnected.
Full scale forward and reflected power range is controlled by the left
METER
switch, selecting 3000
watt
(HI)
or 300 watt
(LO)
. If your transmitter runs more than 300 watts of peak output power, set this
switch to the 3000 watt
HI
(in) position. If your transmitter has less than 300 watts of peak output, set
this switch to the
300 watt
LO
switch position (out). Peak envelope power (PEP) is measured by placing
the
PEAK
or
AVG
push button (middle
METER
button) in the
PEAK
(in) position.
Peak and average power values are equal with steady unmodulated carriers such as closed-key CW,
RTTY, FSK, or FM. The meter reading on these modes will be the same in either peak or average
modes. On SSB, the ratio of PEP to average power varies with different voice and modulation
characteristics. With most voices, the PEP reading is three to five times higher than the average voice
power reading.
Forward power is displayed on the left-hand
FORWARD
meter scale. This scale is calibrated from 0 to
300 watts and is read directly in the 300 watt
LO
METER position. Each picket (scale mark) represents
5 watts below 10 watts, 10 watts between 10 and 100 watts, and 25 watts between 100 and 300 watts. In
the 3000 watt
(HI)
position, multiply the forward power scale 10 times (EXAMPLE: 50 = 500 and 150
=1500 watts).
Reflected power is read on the right-hand REFLECTED meter scale. Full scale reflected power is 60
watts when the meter switch is in the
LO
position , and 600 watts in the
HI
position. This scale is
marked with a picket every one watt below 10 watts and every 5 watts above 10 watts. This scale is also
multiplied by 10 when using the
HI
meter power position.
Power readings are most accurate over the upper half of the meter scales. When measuring power with a
less than perfect match, subtract reflected power from forward power. The result will be the true power.
SWR is read directly from eleven red SWR curves that range from 1:1 to infinity. SWR is measured by
observing the point where forward and reflected meter pointers cross. The SWR is indicated by the red
curve closest to the pointer crossing point. No cumbersome or time consuming SWR sensitivity
adjustments are required with this method.
The power meter and turns counter are backlit with internal lamps. The meter and counter lamps require
power from an external 12 Vdc source. A rear panel jack accepts a 2.1 mm coaxial plug with the center
conductor positive (+) and the outer sleeve negative (-) for powering lamps and metering circuitry. The
negative lead (outer sleeve) is grounded inside the tuner. A meter
ON / OFF
switch turns the meter and
turns counter lamps off and on, and also turns the meter circuitry off when using battery power.
1.3 Antenna
Selector
Summary of Contents for ATR-20
Page 9: ......
